How many of us are using this technique? I really never did it before but am finding that my driving style is changing a bit and I like to be more aggressive. :-B It is also easier on the synchro box. I just wanted to get some opinion from others.
I double-clutch about half the time, usually when I have the energy and I'm not in traffic. :razz: Instead of a Bullitt-lane...they should have a seperate Bullitt freeway...raised up above the others-with no speed limit, of course. Every now and then, there would be a pull out where you could launch your Bullitt off of a ramp if you wanted to: like McQueen on the streets of San Fran. :lol:
I double clutch now exclusively with all downshifts. I learned on my Bullitt and find myself enjoying it on my silly '88 Ranger manual, too.
It is not necessary to double clutch on the upshifts. I'm sure that the pitch of the trans gears mesh with limited synchro action on upshifts. When you downshift, the gear pitch works against getting the gears to mesh, hence the need for synchros. I have learned that the downshift 'whine' or 'ying-a-ying-a-ying' sound is a sure sign that you're wearing your synchros down.
I also figured that when you rev up right before you clutch the second time, it's better to rev the input shaft up a little higher than your final trans motion. That way you can be sure you're on the 'falling' engine speed vs. trans speed side of the mesh, rather than the 'rising' input shaft speed vs. trans speed. Transmissions shift better when the input shaft speed is dropping as the gear is put in place, otherwise the synchros have to start working.
So, even if you double clutch, if you aren't getting that in-between rev up high enough, you might still be wearing on the synchros.
Just remember, if your trans is 'whining', the gears are 'dining.' (Going to lunch!)
Double clutching is the most fun, most professional, and most sensible way to run your sports car. I think I'll head out and do it again!
I have to agree on this one. Once you've mastered the technique, you have no idea how satisfying it is to downshift into, say, 1st gear while rounding a hairpin turn at 20 mph, and being able to get the lever into gear with one finger.
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On 2001-11-26 21:10, 5111 wrote:
What exactly is double clutching?
Think of it this way...
Imagine shifting *without* using the clutch at all. To downshift you would first unload the current gear by adding a small amount of throttle. Next shift to neutral. Now you need to match the speeds of all the rotating parts, the "goes innas" and the "goes outtas". You do this by goosing the throttle a bit more. When the rotating parts are at the same speed you drop it into the new, and lower, gear. And finally you get off of the throttle.
This is what double clutching is trying to do: match up the rotation speeds. Normally this is what synchros do but as the speeds vary more, then synchros start to take longer to do their thing. If you rush it before they are done crunch, clunk, grind!
So the actual sequence goes like this: clutch in, shift to neutral, clutch out, goose throttle, clutch in, shift to lower gear, and clutch out. And if you are real good you can do this while holding constant brake pressure, called heal and toeing.
I don't tend to bother with double clutching except for lower gears. Occasionally on a 3rd to 2nd shift and whenever I want to drop into first above a stop. Again if you look at the gear ratios, this is where you will find the largest jumps from one gear to the next.
Other discussions I have read seem to have concluded that while RPM matching on downshifts is helpful in reducing syncro wear, double clutching is completely unnecessary, and it is redundant to intentionally RPM match on an upshift since RPM's are falling while you shift anyway.
Based on this, I RPM match more or less all my downshifts, though I cannont heel/toe worth anything. However, I've not devoted alot of time to practicing that, as it is difficult to practice in traffic and I rarely put myself into a position where max speed through a corner is important enough that I can't downshift ahead of time.
RPM matching has completely changed the world of manual transmissions for me. While I've always enjoyed manual transmissions, I never learned (or even knew about) RPM matching until after I got #1934. I would always just work the clutch on my downshifts to get a smooth transition, but I never achieved anything like you do when you match RPMs. I enjoy the manual even more than I did before, and I like the fact that I can downshift and have nothing but the change in RPMs give it away.
Listening to some of the autocross guys here during these discussions has made me realize just how much of a gap there is between being pretty good with a manual and mastering it. I'm sure some of them will chime in eventually... :smile:
Also, a bit on double-clutching and rpm matching taken from a longer page:
<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>From David Lane:
Double clutching is really only useful for truck transmissions, which don't have synchromesh gearboxes, and is generally only used when downshifting.
I am not an expert on this, and it is complicated to explain without drawings or a working model, but I can probably give you a mostly accurate description of how it works. In theory, the transmission transmits power from the engine to the car's wheels and tires--we will call them the road wheels for short. In the simplest terms, the road wheels are connected to a single gear in the transmission. There are five gears of different sizes attached to the engine. Each time you upshift, a smaller diameter gear from the engine is meshed with the road wheel gear.
Now, since the road wheel gear can only turn at one rate of speed (depending on how fast you are going) the engine speed must change to accommodate the different gear ratios in the transmission. This is not unlike riding a multi-speed bike. If you go at 10 mph and switch gears, your legs will change speed while your road speed stays the same.
It would be damn difficult to change gears if the engine were always connected to the transmission. Fortunately, when you depress the clutch, the engine is disconnected from its gears. When you push the shifter to the next gear, there are "synchromesh rings" in front of the gear which matches the speed of the engine-driven gears to the speed of the road wheel gear--speeding the engine-driven gears up, or slowing them down as necessary. Once the synchromesh gets the two gears going at the same speed, the teeth will mesh and the shift is accomplished. Without synchromesh, if the two gears are not going at the same speed, the gear teeth will grind against each other, which is not good for the transmission. You have no synchromesh in reverse, which is why you have to be stopped to shift there. If you are rolling forward, the road wheel gear will be moving, and you will hear a grind.
Anyway, double clutching is a way to match the engine speed in a given gear to the road wheel speed, in a transmission without synchromesh. In a downshift, you depress the clutch and come into neutral. The engine needs to be going at higher rpms to accommodate the speed of the road wheel gear, so you let the clutch out (still in neutral)--which re-attaches the engine driven gears to the engine. Then you blip the throttle to increase the engine speed, which gets the engine-driven gears spinning faster, until they are going at the right speed to mesh with the road wheel gear. You push the clutch back in, and if you have done it right, the shifter will move easily into the lower gear. If you miss, you will hear a lot of grinding and probably a lot of cursing will come from your lips. Oh, well. That's why they have truck driver's school. Let the clutch out, and you are on your way.
As you can see, synchromesh makes the whole process much easier. When downshifting, you can hold the clutch in just once and blip the throttle, which will do some of the work for the synchromesh and make the mechanical parts last longer. If you are not exactly on target, the synchros will do the rest of the work for you.
Now you can see why upshifting does not require any fancy clutch work. When you upshift, the engine slows down between gears. It will do this anyway as soon as you take your foot off the accelerator and depress the clutch. If you pause for a moment in neutral, it will give the engine a chance to slow down enough to align the gears, and the stick will easily slip into the next higher gear.
If you are in a race, push harder on the stick and go directly from gear to gear. The synchros will match speeds for you.
In the broadest view, all we are talking about is smooth driving and saving some wear and tear on the synchromesh. There are a lot of old ladies out there who have never heard of any of this, and who's transmissions last a good long time. Performance drivers are much more likely to stress their cars, so they tend to find ways to make less work for the transmission if possible.
Here is an experiment for you. Go out on a road where you have some room. Put the car in third and go at about 3000 rpm. Maintain speed and see how fast the engine is going when you shift to forth. let's say it is about 2200 rpm. Now go back into third at 3000 and put a little pressure (one or two fingers) on the shifter toward neutral. Don't depress the clutch. Nudge the accelerator a little to remove the tension between gears, and the the stick will move out of gear, into neutral. Take your foot off the accelerator, and put a little pressure on the stick toward forth gear. When the engine rpm drops to 2200 rpm, the stick will probably slide into forth without you ever pressing on the clutch. If you miss, and the engine rpm drops below 2200, just give it a very little gas to get it back to that speed. When the engine speed matches the road wheel speed, it should drop into gear. That should illustrate how it works. Be real gentle with the shift lever, and you won't hurt anything. Push too hard, and you will hear a grind.
It is more difficult doing this trick going from forth to third, but all you have to do is use the accelerator to raise the engine speed while in neutral. Very few drivers know how to shift without the clutch, and I offer this description to you for your amusement and experimentation. Obviously I won't be responsible if you break something--although if you stay gentle with the shifter, the worst you may experience is a little, soft grinding sound. If you hear that, go back to neutral and either try again, or give up.
I had to learn this trick when I blew my clutch at an autocross, thirty miles away from home. It was my own fault, I lost track of how fast I was going and tried to downshift into first, which over-reved the engine and disintegrated the clutch friction surface. I actually drove the car home, matching gears, without ever using the clutch. I had to go real slow near stop lights, and once or twice I had to stop the car and start it in first gear to get going again. That was in the days before cars had to have the clutch pedal pressed in order to start them. </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>
Another 'oldie but goodie' brought back from the dead??
Double clutched years ago in old trucks and British sports cars without synchromesh but today only rarely when downshifting at speed in a tight corner (matching revs to keep the rear from breaking away). Nissan does this for you in the 370Z with its 'synchro-rev-match' feature. Tried it and hated it but it can be disabled with a button on the console. In my opinion there's no need to double clutch in ordinary driving unless you just want to exercise your left leg!
I have gotten into the habit of double clutching when downshifting. Not needed but I just like to hear the engine rev.
In previous cars, I got into the habit of not using the clutch except to take off. Did all the upshifts and downshift using the rev matching and letting the transmission just pull itself into the gear. I ended up putting over 200,000 miles on each of these cars, so no, it is not hard on a transmission if done correctly.
If I drove the B as a DD, then I might start the clutchless driving but for the little time I drive the B, I just have never gotten to the point where I get the feel for the correct revs and pressure that required.
Imo, I don't feel the need to go clutchless. Not like these trannies are syncro-less...Let the dang thing do it's job. As for shifting without a clutch, I have owned a couple cars that were syncro-less. A 1962 Fairlane with a three speed column shift. The clutch actually went out in that car and I drove without a clutch for a couple weeks. I also had a 1964 VW microbus. It had a slick tranny. Say what you want about the VW's, they had a great transmission. So good, that it would encourage the shifting without a clutch. Syncros were in all forward gears of all cars sold stateside starting in 1959, IIRC. But, the transmission was so slick, you only needed to clutch while sitting at a light, or changing from reverse to forward.
Double clutching, is a lost art. But it's important to realize, you're wasting your time. Unless your clutch has gone south.
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